Electric fuse and fuse holder



July 23, 1940. BUSSMANN 2,209,048

ELECTRIC FUSE AND FUSE HOLDER Filed July 20, 1936 2 Sheets-Sheet 1 as 50%'Z' INVEN TOR. Hz. 0 KS/ Us .15. BussMA/v/v ATTORNEY July 23, 1940.BUSSMANN 2,209,048

ELECTRIC FUSE AND FUSE HOLDER Filed July 20, 1936 2 Sheets-Sheet 2INVENTOR. HL 0 rsws B. ,BussMfiN/v A T TORVE Y Patented July 23, 1940-UNITED STATES PATENT OFFICE ELECTRIC FUSE AND FUSE HOLDER Aloysius B.Bussmann, St. Louis, Mo.

Application July 20,

44 Claims.

My invention relates to thermal protective devices designed to form partof an electric circuit for the purpose of protecting such circuit byinterrupting the circuit when subjected to harmful overloads.

In referring to my invention, I use the terms fuse and fuse holder. Itwill be obvious to those versed in the art that a thermal cutout orcircuit breaker or other form of protective device might be used inplace of a fuse and my invention is intended to cover any form ofelectrical protective device capable of being associated with my fuseholder.

An object of my invention is to provide a fuse holder and a(so-operating fuse which make dimcult the bridging, shunting or shortingout of the fuse by a foreign electric conductor inserted in the holderin parallel with the fuse.

Another object of my invention is to provide a fuse holder and aco-operating fuse that make it difficult to use a fuse of greatercarrying capacity than that for which the holder is designed.

Another object of my invention is to provide such fuse holder in theform of a receptacle. By 5 receptacle I mean a fuse holder havingpermanently attached contact terminals for connection to the wiring ofan electric circuit such as a. fuse block, panel-board, fused switch andthe like.

Another object of my invention is to provide such fuse holder in theform of an adapter for use in the Edison fuse holders already installedat the present time to permit of obtaining the above desired objects inold installations.

Another object of my invention is to provide a fuse assembly whichpermits of obtaining the above desired objects without impairment of thecurrent-carrying, overload-blowing or short-circuit-protective operatingcharacteristics required of standard fuses.

Another object of my invention is to provide such a fuse assembly whichdoes not depend for its eflicacy on dimensional exactitude of itscorrelating parts beyond what is ordinarily found in commercialmanufacturing.

Another object of my invention is to provide a fuse which permits ofobtaining the above desired objects which can be manufactured at a costcomparable to that of plug fuses such as are now in common use.

Other objects of my invention will more fully appear from the followingdescription and accompanying drawings of devices embodying my inventionin the forms now preferred by me, and will be pointed out in the claims.

Many of the users of electricity apparently do 1936, Serial No. 91,492

not appreciate the importance of the protection afforded by a fuse. Someof them feel that the blowing of a fuse is a waste of money. Others seemto feel that the inconvenience caused by a fuse blowing is not offset bythe protection obtained. Still others will resort thoughtlessly to theuse of a substitute when a fuse blows and they have no other to replaceit. Even where owners fully realize the importance of the fuse, carelessor thoughtless employees often resort to substitutes for fuses,sometimes to prevent their being inconvenienced by the blowing of thefuse, sometimes because of a desire to economize for their employer, orfor other reasons.

Eliminating the blowing of fuses of course also eliminates theprotection needed for electric circuits. Few of those who endeavor toprevent the blowing of fuses seem to realize the grave fire hazardscreated by their actions but records show that such actions result inlosses amounting to millions of dollars of property annually andsometimes human lives.

The easiest way for the user to prevent or reduce the blowing of fusesis to use fuses of too large a size. A fuse having a carrying capacitygreater than the carrying capacity of the circuit in which it isconnected obviously cannot protect that circuit. Yet fuse receptacles inuse up to the present time are so designed that the same receptacle willtake many different sizes of fuses, so that a fuse of too great acurrent carrying capacity for many circuits can be inserted therein. Inmy new fuse and fuse holder, means are provided to make sure that when afuse holder of the correct size is attached to the circuit, it isimpossible to insert therein a fuse of too large a size.

Preventing the blowing of fuses by using substitutes is however stillmore hazardous. In such cases, the user may insert a metal disc, or awire, or tin foil, or some of the metal parts of the fuse itself in sucha manner that the fuse is partially or entirely eliminated from thecircuit. What is particularly vicious is the fact that such substitutionis made in the bottom of the fuse recepta- 45 cle and in such a mannerthat, with the fuse installed, the tampering is not at all visible, sothat, even if such particular electrical installation should beinspected, the inspector could not feel sure that proper fuse protectionhad been pro- 50 vided unless he removed each and every fuse from itsreceptacle and examined each of them.

Much has been done to design enclosed switches and fuse receptaclepanels to make it practically impossible for the user to obtain accessto any 55 x 1 connections that would permit him to install jumpers toby-pass, not alone the fuse, but the fuse receptacle as well. All ofthis, however, is useless if the fuse can be by-passed within the fusereceptacle itself.

The receptacles in use heretofore for holding the ordinary type of plugfuses are so made that it is a simple matter. to insert a metal disc,such as a penny, in the receptacle and then by means of a fuse to holdsuch disc in place and thereby by-pass the fuse. This is prevented in mydevice.

Designing the fuse receptacle to prevent the use of such metal discs ishowever not sufdcient. Fine wires such as the strands of a lamp cord,could be resortedto. Preventing the use of fine wires and metal discs isnot sumcient because tin foil could then be employed as is already thepractice with some of these short sighted users. Tin foil is alwaysreadily available. Its extreme thinness, flexibility and almostself-lubricating property makes it a reasonably easy matter to bypassplug fuses known to the art up to the present time. My new fuse and fuseholder, however, makes it difficult or impossible to by-pass the fusewith either tin foil or wire and impossible to do so with a coin.

In the drawings,

Figure lis a view, in longitudinal section, through a receptacleembodying my invention,

Figure 2 is a view, in longitudinal section, through an adapterembodying my invention,

Figure 3 is a view in side elevation thereof,

Figure 4 is a view in side elevation 'of a fuse embodying my invention,

Figure 5 is a view in longitudinal section therethrough,

Figure 6 is a view, partially in side elevation of a fuse holder, with afuse in position, both embodying my invention,

Figure '7 is a fragmentary-view in longitudinal section of a fuse holderhaving a resiliently-supported center contact,

Figure 8 is a top plan view of a metal spacer and screw thread ring,

Figure 9 is a view in diametral section therethrough,

Figure 10 isa view in front elevation of a screw thread ring used in thetubular member shown in Figures-11 and 12,

Figure 11 is a top plan view of one-half of a tubularelectric-insulating member constituting a part of the holder shown inFigures 1 and 2,

Figure 12 is a view,- in front elevation, of the member shown in Figure11,

Figure 13 is a bottom plan view of a fuse body,

Figure 14 is a view, in side elevation. of a screw disc adapted to bemounted *on the fuse body of Figure 13,

' Figure 15 is a. bottom plan view thereof,

. Figure 16 is a top plan view of a screw thread ring used in thetubular member shown in Figures 11 and 12.

Referring now to Fig. l of the drawings, I have there illustrated areceptacle having a block 2%v particularly by reference to Figs. 8 and 9of the drawings. This screw thread extends through substantially oneturn, but may be of slightly more or less than this peripheral extent.The leading end 30 of the screw thread is relatively abrupt or salient.

Slightly below this there is a screw thread 3| provided with saw teeth32 in its inner edge and with a salient leading end 33.

Still further down in the well of the receptacle are two threads 34 and35. These are shown-as plain metal rings, but provided with a'salientleading end 36.

At the bottom of the well is an insulating disc 31 having anaperture'38, and a resilient disc 38 provided with a central aperture40. Beneath this disc is electric insulating material 5! with a recess42 and provided with a central aperture within which is located contactmember 45 to make electrical contactwith the fuse. The other contact forthe fuse is at 65.

The disc 39 as well as the threads 2B, 3!, 3d, 35 are preferably allelectrically insulated from each other and from the contacts as and 65.

Figs. 4 and 5 illustrate a fuse adapted to co-= operate with thereceptacle shown in Fig. l. The fuse comprises a body ltd ofelectric-insulating material having a portion are adapted to fitwithinthe receptacle and a shoulder m3 which does not enter the well 2'?of the receptacle. At one end of the fuse is a contact member iii- Atthe shoulder W3 is a contact member N2 of U shape which extendspartially annularly around the portion m2. Portions of this contactmember H2 are located closely adjacent to the shoulder its while otherportions thereof are bent away therefrom as shown at 5 E3 to make thiscontact member resilient.

The contact members iii and H2 extend into the body of the fuse andtotheir respective inner ends is attached a. fuse link in. While I haveillustrated a simple fuse link, I do not desire to be limited thereto,as has hereinbefore been set forth. The fuse may include further atransparent disc H8 at the outer end held in place by a metal cover it 9as shown.

The body portion 32 is provided with screw threads 685, preferablyintegral with the body of the fuse. I

At the lower portion it? of the body there is provided a single screwthread E06 having a leading end It! which is relatively abrupt andhaving the outer edge adjacent to this leading end provided with sawteeth or serrations M18 as shown in Figs. 14 and 15.

I preferably but not necessarily insulate the thread I66 from thecontact Hi.

It is to be noted that the external diameters of the screw threads onthe fuse are but slightly less than the internal diameter of the well2'! and that the thickness of the threads on the fuse is butslightlyless than the space in the threads 2?, iii, 36, 35, whereby relativelysmall clearances are provided between the fuse and the well 21, it wouldnot make contact with the me ber 44. The presence of the disc would alsoprevent the fuse from entering the thread 35 which holds the fuse inposition in the receptacle. Assuming that the fuse could be held in thereceptacle in some manner, while a disc is in the well, there would betwo gaps in the circuit, one from the member 44 to the bridging disc,another from the disc to the top contact 45. The difficulty ofattempting to place conducting material in these gaps will be shownlater. If the last mentioned gap were bridged, it would not be held intight contact because the shoulder I03 or the contact H2 of the fusewould not be down far enough. Hence it would be necessary to place somematerial at this point to hold the bridging in contact. Such materialwould bein the open, where it would be quite plainly visible toinspectors, meter readers, service men and the like.

Another method of attempting to bridge the fuse might be by placing astrip of flat thin metal along the portion I02 of the fuse. Even thoughsuch strip were formed to fit the contour of the fuse body and thevarious threads as closely as possible, it would be found in turning thefuse body to engage the thread 28, that because of the relatively smallclearance and because of the salient leading end 30 of this thread thatthe strip would probably be pulled out of position. However, assumingthat the strip did get through this particular thread, it would thenencounter the salient leading end 33 of the thread 3| where it wouldprobably be pulled out of position. About that time also, the additionalthreads H85 on the fuse body would be engaging thread 283, adding to thestrain on the metal strip and making it still more difficult to keep itin proper position.

If however, all of these diificulties were overcome, the strip muststill stay in position when the thread M6 on the fuse body encountersthe salient leading end 36 of threads 34 and 35 and must pass throughthe extremely small clearance in those threads. Assuming that this werepossible, the strip would then have to be making tight engagement on thecontact iii because of its being insulated from the thread 806. Duringsix, seven or eight revolutions of the fuse through all of these guards,the strip of metal would have to remain in position, if the attempt tobridge or shunt the fuse were to be successful. The strip wouldobviously be caused to take up a tortuous shape in the receptacle andbetween the receptacle and the fuse whereby the scraping, cutting orsevering action at a number of points and the number of points at whichthis action takes place are both greatly increased.

It is also obvious that placing such a strip of thin metal in thereceptacle and then attempting to insert the fuse would not in any wisedecrease the difiiculties of bridging the fuse in this man ner, and thatno different result could be looked for.

Another method of attempting to bridge the fuse might be to use finewires, such as those found in flexible cords or lamp cords. Wrappingseveral of such fine wires around a portion of contact H2 of the fuse,then forming them to the contour of the fuse, over all the threads ofthe fuse and then around the contact III, the next problem would be toscrew the fuse into position so that such bridging would extend from thecontact 44 to the contact 45 on the receptacle. Here again it would befound in turning the fuse body to engage the thread 28, that because ofthe relatively small clearance and more particularly because of thesalient leading end of this thread, that the wires would probably bepulled out of position. If they did get past the salient leading end ofthe thread, the wires would still have to pass over the saw toothserrations 29 on this thread, each tooth oi which would be aconsiderable hazard for such wires.

If one succeededin getting these fine wires past these hazards, thewires would be released as soon as the thread 106 of the fuse passed outof the thread 28. Being discontinuous, the threads in the receptacle donot hold such bridging material tightly in position to thereby beassisted in passing thru the next thread. At each revolution of the fusesuch material is passed over the hazards of one of these threads, thenreleased and then again subjected to a new hazard.

After passing out of the thread 28, the salient leading end 33 and theteeth 32 entirely around the inside of the thread 3| would then beencountered and if there should be any one of the wires remaining inposition, it may be assumed that the salient leading end 36 of thethreads 34 and 35 would sever it. Even if a wire got through here, itwould still have to pass through the extremely small clearance betweenthese threads in the receptacle and the thread it on the fuse. It istherefore easy to see how extremely difiicult it would be for any wiresto have remained intact during the six, seven or eight revolutions ofthe fuse necessary to put it in position. The exact number ofrevolutions depends of course on the pitch of the threads used, whichpreferably would be l2, 14 or 16 to the inch. The portion i112 beingapproximately one half inch long, the number of revolutions would haveto be as stated.

If the fine wires previously referred to were wrapped around the body ofthe fuse, instead of being formed to the longitudinal contour of thefuse, no better result could be expected by the bridger because thethreads I05 on the portion )2 would push the wires into engagement withthe various salient leading ends of the threads in the receptacle andwith the saw teeth serrations on these various threads so that duringthe entire period of each revolution, these wires would be subjected toa tearing, cutting or severing action. a

In this connection, it must be borne in mind that the very naturalunsteadiness of anyone attempting to screw in the fuse with bridgingwould serve to constantly cause the fuse and the bridging material to bepushed against these various hazards. The more the fuse and bridgingmaterial might be held, for a moment, away from one hazard the more itwould be pushed against the hazard on the opposite side of thereceptacle. There is nothing in this device to serve to steady the handof the bridger. From the moment ,he attempts to engage the first screwthread 28 until the fuse is finally in position it is moving from oneside to the other and not being guided or held away from any of thehazards created for any of the bridging material or methods that mightbe used.

If the fine wires previously referred to were placed in position in thereceptacle before any attempt were made to put the fuse in position, itis easy to see that the difliculties encountered in attempting to bridgethe fuse would be just as great, if not greater, than those alreadymentioned.

One more method that might be tried to bridge a fuse would be by meansof metal foil. It might be wrapped carefully and tightly around theportion I02 of the fuse or applied to the fuse in many to the samesevering, cutting, tearing and scrapplies particularly when metal foilis used. I refer ing action at almost every point in the entireinserting operation as above outlined. Tests show that such foil is cutup into many fine particles. Sometimes, after such an attempt, it ispossible to get a small amount of current through the bridging for justa flash. The fofl however, will have been so badly cut up that thecarrying of any reasonable amount of current for more than a moment isimpossible.

An additional safeguard is included that apthe same diameter as thecontact III which passes through it. The small aperture, plus the factthat there is a recess 62 between the insulating material 8| and thedisc 38 when the fuse is out of the receptacle, makes the filling orpartial filling of the space down to the contact to extremely diflicult.A very small tool would have to be used to get into the aperture andinfinite patience and care would have to be exercised to get enoughfoil, solidly packed, within this space to be of any help in bridgingthe fuse holder or the fuse. Naturally, even if the space referred towere filled solidlywith foil, it would still be necessary to bridge allof the balance of the fuse holder well, or all of the portion 32 of thefuse.

This disc 39 is left loose and is made resilient. Drilling the aperturelarger is practically impossible because of the resilient nature of thedisc and because it is not tightly held in position. Furthermore, ifthis disc were tightly held in position, or were not resilient, it wouldoften be impossible to insert the fuse in the receptacle,

. because the natural variations that occur in manufacture and assemblywould result very often in the contact 1 H not being exactly in linewith the aperture All. As it is, the contact ill of the fuse oftenengages the top of the disc, but the disc being left loose and beingresilient, the pressure applied by screwing in the fuse pushes down thedisc and moves it laterally so that the fuse contact can enter in spiteof the very small clearance, and make proper electrical contact oncontact Gil.

If an attempt were made to bridge the fuse, without inserting the fuseinto the receptacle as far as it should go, it would not of course enterthe threads 34, 35 which are the means for holding the fuse sufficientlytightly in position to make good electrical contact. No matter how muchforeign material might be used in attempting to bridge a fuse, goodcontact would be necessary to prevent useless interruptions caused bythe heating of such contact from the current normally flowing in thecircuit. Hence, putting the fuse loosely in position with such bridgingmaterial would avail nothing. If it were possible to put it in tightly,with such bridging material, without turning the fuse the full six,seven or eight revolutions, the contact H2 or the shoulder M3 the fusewould not be down far enough to insure the bridging material being incontact with the contact 45 of the receptacle, so that some additionalmaterial would have to be used on the outside of the receptacle, whereit would be plainly visible.

The devices embodying my invention thus provide a tamper-proof fuse andfuse holder which make it extremely difficult to short circuit the fuselink or to substitute for a blown fuse any foreign electric conductor,the receptacle being provided with means for severing the continuity ofa foreign electric conductor located on a fuse screwed into thereceptacle and the fuse being provided with means for severing thecontinuity of a foreign electric conductor inserted in the receptaclebefore the plug is operatively associated therewith.

It is obvious that the substitution for a fuse of proper capacity of afuse having a smaller current carrying capacity will not constitute afire hazard or endanger the energy translating devices which may beprotected thereby; but it is desirable that the design and constructionof the various plug fuses be such as to prevent the insertion in thefuse holder of a fuse having a fuse link therein of a greater continuouscurrent carrying capacity than that of the circuit in which it isconnected.

I therefore use different threads on different sizes of fuses whichshould not be interchangeable. For example, I may use 16 pitch threadson fuses up to 6 amperes, 14 pitch on fuses from I to 15 amperes and 12pitch on fuses from 20 to 30 amperes. I may also use left hand threadsor double pitch threads on some sizes and thus obtain furtherdifferentiation. Corresponding changes in the screw threads of the fuseholder must, of course, be made so that fuse and fuse holder maycooperate properly.

In addition to this, I may use stop lugs in the bottom of the receptaclewell, to further limit the size fuse that might be used in receptaclesdesignated for amperages of certain limits. I accomplish this byproviding on the lowermost screw thread 35 a stop lug 55, as shown inFig. 16.-

This lug is located in a predetermined position axially of thereceptacle. The leading end ill? of the screw disc W6 is adapted to abutagainst the leading side of stop lug 55 when the fuse has been-screwedinto the receptacle. If the leading end of the screw disc are on acertain size fuse abuts against the stop lug before the member ill is incontact with the member M5, it is obvious no current will flow and suchfuse would be useless in such receptacle.

For example, if I use 14 pitch threads on 7 to 15 ampere fuses I may puta stop lug on receptacles intended for fuses not larger than 8 amperes.In that event I lengthen the contact ill on 8 ampere fuses, so that whenthe screw disc Hi6 abuts on the stop lug, the longer contact Ill will bein contact with the member t6 and be in operative position. The 15ampere fuse having the same threads could be inserted in the samereceptacle, but having a shorter contact Ill would not be able to makecontact with the member it, because its screw disc Hi6 would be stoppedby the stop lug and prevent the fuse being screwed down all the way. 10ampere receptacles might be arranged with the stop lug in a slightlydifferent position and with the contact ill slightly shorter than thatof the 8 ampere fuse but longer than that of the 15 ampere one.

Thus, another method of preventing the use of incorrect sizes of fusesis provided at practically no cost.

It is obvious that several different forms of construction might be usedin building fuses and 75 fuse holders embodying my invention. I haveshown the form of construction preferred by me at this time. In thisconstruction, the fuse holder comprises a metal ring 6|, twosemi-annular members 62 of electric-insulating material and a disc 4| ofelectric-insulating material held together by a metal shell 63. Themembers 62 are shown particularly in Figs. 11 and 12 of the drawings.Each is provided with peripheral grooves or recesses 64 in the bodythereof at the inside surface. The axial location of these peripheralrecesses varies slightly in the two members, to the end that they maymatch properly, when the two members are placed in abutting position tohold the relatively thin metallic sheared rings 3|, 34 and 35 inscrew-thread formation. The axial spacing of these grooves is such thatthe latter constitute, when assembled in the grooves, an interruptedhelical screw thread, of which screw thread 28 also forms a part. Theends 33, 36 of the respective screw threads 3|, 34 and the leading endof the screw thread 28 are adapted to be located in peripheral alignmentas shown in Fig. 2 with one of the diametral faces 65 of thesemi-annular member 62, as is shown in Fig. 11 of the drawings. Theinitially flat rings 3|, 34, 35, will then have the shape shown in Fig.10 of the drawings, the axial distances between the two ends of the ringcorresponding to a predetermined pitch. Instead of using continuousscrew threads, I may use interrupted screw threads comprising properlyspaced projecting lugs. The leading ends of the screw threads may beconsidered as projecting lugs.

The metal ring 6| having the screw thread 28 formed on its inner surfaceis made heavy and relatively long axially, the proportion of its axiallength to the total length of the holder being substantially that shownin the drawings. The purpose of this is to prevent partial destructionof the fuse holder which might permit of bridging of the fuse or the useof an over-size fuse. The size of the ring is such that destructionthereof is diflicult if not impossible. Removal thereof from the shell83 will leave all the remaining parts loose in the shell, particularlythe members 62 holding the threads 34, 35, thus preventing the holdingof the fuse in the fuse holder in operative position. There would benothing then to hold the fuse in tight contact with the contact 44 andthe resilient disc 39 would even push the fuse away from such contactmember. This ring is provided with an axially extending lug 66 at oneside adapted to fit into a recess 61' provided in one of thesemi-annular members 62 in order that the member 6| may have adefinitely fixed position relative to the tubular body comprising thetwo portions 62. The ring GI is preferably insulated from the shell 53by insulation 10 in the form of an insulating washer or a coating ofinsulating paint, so as to insulate this ring from the contact 45.

The insulation material 4| is in the form of a disc and has an axiallyextending lug 68 to interflt with recess 69 on member 62. Thisconstruction enables members 6|, 62 and 4| to be held together as asingle unit in which rotation of any one of the members relative to theother is prevented. I

Seated thereon is the resilient disc 39, preferably but not necessarilyof metal, which when the fuse is in position is pressed down in therecess 42.

The shell 63 is turned over the ring 6| to form the upper contact 45 ofthe fuse holder, It is obvious that this contact need not be continuousand need not extend through substantially 360 degrees.

In building my preferred construction of the fuse, I provide a metalwasher I30 between the contact III and the screw disc I03 which metalwasher is covered by insulation I3I in the form of an insulating washeror a coating of insulating paint, so as to insulate the screw disc fromthe bottom contact. This washer is of course held by the bottom contactIII.

It is obvious that manipulation of the fuse body itself might beattempted to bridge the fuse. It is for this reason that I prefer thefuse body of a frangible material, such as porcelain, so that operationthereon will soon damage it beyond possibility of use in the receptaclein any way that would make the bridging operative.

The fuse body has a short projecting inner end I32 which may have anirregular polygonal periphery as is shown in Fig. 13 of-the drawings.The screw disc I06 is provided with an opening I33 of the same contouras the end I32 so that the disc will fit in a definite position thereon.It will be obvious that the polygonal end I32 on the fuse body must bedefinitely located relatively to the threads I 05 and that the polygonalopening I33 must be definitely located relative to the thread on thedisc I36 in order that the single screw thread on the screw disccooperates properly with the screw thread I05 to constitute a singlehelical screw thread.

Where fuses having different threads are used, the projecting ends I32of the bodies are of different contours, the polygons having differentnumbers of sides, and the screw discs different openings I33 to lit theprojecting ends of the bodies.

I may also arrange for a movable circuit breaking contact member at thebottom of the receptacle well 21, as shown in Fig. '7 by attaching tothe resilient disc 39 substantially centrally thereof a contact member8| of such size that when the fuse is out of position and the disc isflat, this contact will be out of engagement with contact member 44, butwhen the proper fuse is in place, this contact will be in closeengagement with the contact member 44. This disc is preferably so madethat it has suflicient strength to prevent the contact 8| from beingheld in contact with the contact 44 by the pressure of bridging materialwhich might be packed in the fuse holder. This adds to the difliculty ofbridging as it would make necessary not only bridging between contact 8|and 45, but holding the spring disc down as well.

To permit of my invention being used in old installations, I may make myfuse holder in the form of an adapter designed to permit the use oi. myfuse in plug fuse receptacles already installed. This adapter is shownin Figs. 2 and 3. It will be noted that instead of the plain shell 63, Iuse a screw shell 63A which holds in place parts similar to those thatconstitute the fuse holder in my receptacle shown in Fig. 1 except part4|. Instead of part 4| I use a part 4IA of slightly different shapewhich serves the same purpose. The shell 63A is turned over the ring GIand is also turned over against the lower angularly inclined surface I3of disc A whereby the semiannular members 62, the upper ring 6|, theinsulating disc 31, the resilient disc 39 and the insulation disc 4| Aare held in tightly assembled operative positions relative to each otherto make a solid, compact unit for easy insertion in old receptacles. Theadapter has attached thereto some form of locking means wherebywithdrawal of the adapter from the receptacleis prevented after it hasonce been inserted'therein, as shown at M.

Where I use the term bridging .a fuse in the specifications and claims,I mean the bridging of the terminal contactspf the fuse or of the fuseholder whether or not the fuse link is blown. Where I use the words fuseholder it is to be understood that this term covers an adapter as wellas a receptacle. Various modifications may be made in the devicesembodying my invention without departing from the spirit and the scopethereof, and I therefore desire that all such modifications shall becovered by the appended claims, which are to be limited only by theprior art.

I claim as my invention:

1. A plug fuse having a bodyadapted to be operatively engaged with afuse holder by relative rotary movement, said fuse having meansextending abruptly and substantially radially from the lateral surfaceof the body to break the continuity of a'foreign electric conductorpositioned to bridge the fuse within the fuse holder.

2. A plug fuse adapted to be operatively engaged with a fuse holder andhaving an abrupt projection extending laterally outwardly from the fuseto engage with and. impair the conductance of a foreign electricconductor positioned to bridge the fuse while being engaged operativelywith the fuse holder.

3. A plug fuse adapted to be operatively engaged with a fuse holder and.a toothed member extending laterally outwardly from the fuse to engagewith and impair the conductance of a foreign electric conductorpositioned to bridge the fuse while being engaged operatively with thefuse holder.

- 4. A plug fuse having a body adapted to be operatively engaged with afuse holder, a fuse link substantially enclosed in said body, axiallyspaced contact members extending through the walls of the body andtransversely projecting means on the body positioned axially between thecontact members to break the continuity of av foreign electric conductorpositioned to bridge the fuse within the fuse holder.

5. A plug fuse adapted to be operatively engauged with a fuse holder byrelative rotary movement, said fuse having means extending laterallyoutwardly therefrom comprising an abrupt leading surface to engage withand impair the conductance of a foreign electric conductor positioned tobridge the fuse while being engaged operatively with the fuse holder.

6. A plug fuse having a body adapted to be inserted in a fuse holder, 2.member on the body extending approximately laterally outwardly from theperipheral surface thereof and having an uneven outer surface to breakthe continuity of a foreign electric conductor positioned to bridge thefuse within the fuse holder.

7. A plug fuse adapted to be operatively engaged with a fuse holder anda member carried by the fuse adapted to engage a thread on the fuseholder and having an abrupt projection ment, said fuse havingmeansprojecting substantially radially outwardly from the peripheralsurface of the body comprising an abrupt leading edge to break thecontinuity of a foreign electric conductor positioned to bridge the fusewithin the fuse holder.

9. A plug fuse having a body adapted to be inserted in a fuse holder byrelative rotary movement, said fuse having a disc on the body with anabrupt radially-extending portion constituting a leading edge in therotary movement to break the continuity of a foreign electric conductorpositioned to bridge the fuse within the fuse holder. 1D. A plug fusehaving a-body adapted to be inserted in a fuse holder, said fuse havingmeans projecting substantially radially outwardly from the peripheralsurface of the body adapted to hold the fuse in a fuse holder, saidholding means being designed and constructed to break, during insertionof the fuse in the fuse holder, the continuity of a foreign electricconductor positioned to bridge the fuse within the fuse holder.

11. A plug fuse having a body adapted-to be inserted in a fuse holder,said fuse having a disclike member projecting radially outwardly beyondthe peripheral surface of the body adapted to hold the fuse in a fuseholder and to break, during insertion of the fuse in a fuse holder, thecontinuity of a foreign electric conductor positioned to bridge the fusewithin the fuse holder.

12. A plug fuse having a body adapted to be inserted in a fuse holder,said fuse having a screw-disc projecting outwardly beyond the outer.

peripheral surface of the body adapted to' hold the fuse in a fuseholder, said screw disc having an abrupt leading edge to break, duringinsertion of the fuse in a fuse holder, the continuity of a foreignelectric conductor positioned to bridge the fuse within a fuse holder.

13. A plug fuse including a body, axially-spaced contact membersthereon, one of which is of relatively short axial extent exterlorly ofthe body and means adapted to break the continuity of a foreign electricconductor positioned to bridge the fuse within a holder when the fuse isfitted therein, said breaking means extending radially to a distancefrom the axis of the fuse, intermediate in value between the radialdistances to which the respective contact surfaces extend and axiallypositioned between said contact sur-' faces.

ii. A plug fuse as set forth in claim 9 in which the disc hasinter-fitting engagement with a portion of the body.

15. A plug fuse having a body adapted to be inserted in a fuse holder,said fuse having a disc-like member projecting beyond the outerperipheral surface of the body adapted to hold the fuse in the fuseholder, said disc-like member having interfitting engagement with aportion of the body and having component parts of different radii and ofdlfferent axial displacement to break. during insertion of a fuse in afuse holder. the continuity of a foreign electric conductor positionedto bridge the fuse within the fuse holder.

16. A fuse holder comprising a shell of electricinsulatlng material anda discontinuous screw thread held by the insulating shell and adapted tohold a plug fuse in the fuse holder.

17. A fuse holder comprising a shell of electric-insulating material anda discontinuous screw thread held by the insulating shell and havingabrupt leading ends adapted to break the continuity of a foreignelectric conductor positioncd to bridge a fuse within the fuse holder.

18. A fuse holder comprising a shell of electric-insulating material anda series of discontinuous screw threads held by the insulating shell,one of said screw threads being adapted to hold a plug fuse in the fuseholder and one of said screw threads having an abrupt leading endadapted to break the continuity of a foreign electric conductorpositioned to bridge the fuse within the fuse holder.

19. A fuse holder comprising a shell of electric insulating material; ametal ring at one end thereof, an apertured disc of electric-insulatingmaterial at the other end of the shell, 9. metal shell enclosing saidshell of insulating material and said metal ring and clamping them andsaid .disc together and a discontinuous screw thread supported by theinsulating shell and adapted to hold a fuse in the fuse holder, saidmetal ring having means thereon comprising a screw thread having anabrupt leading end thereon adapted to break the continuity of a foreignelectric conductor positioned to bridge the fuse within the fuse holder.

20. A fuse holder comprising a shell of electric insulating material, arelatively thick metal ring having a screw thread thereon and positionedat one end of said insulating shell, an apertured closure disc ofelectric-insulating material at the other end of said shell, relativelythin split metal rings supported by said shell and cooperating with thescrew thread on the metal ring to form an interrupted screw thread, anda metal shell clamping together said metal ring, insulating shell andclosure disc, said metal rings being insulated from said metal shell andfrom each other. 7

21. A fuse holder comprising a shell of electricinsulating material, ametallic member in the side wall of said shell adapted to detachablyhold a plug fuse in the fuse holder, said metallic member being free ofcurrent flow therethrough.

22. A fuse assembly comprising in combination, a fuse holder and a plugfuse insertible in the fuse holder, said holder and fuse each having adiscontinuous screw thread adapted to break the continuity of a foreignelectric conductor positioned to bridge the fuse within the fuse holder.

23. A fuse assembly comprising in combination, a fuse holder and a plugfuse insertible in the fuse holder, said holder having a discontinuousscrew thread and said fuse having means cooperating with the screwthread adapted to detachably hold the fuse in the fuse holder and tobreak the continuity of a foreign electric conductor positioned tobridge the fuse within the fuse holder.

24. A fuse assembly comprising in combination, a fuse holder member anda fuse member adapted for co-operative inter-fitting engagement with thefuse holder member, one of said members having a projection on an axialface adapted to catch in the surface and break the continuity of aforeign electric conductor positioned to bridge the fuse within theholder.

25. A fuse assembly comprising in combination, a fuse holder, and a fuseinsertible in the fuse holder, said holder and fuse respectivelyincluding a discontinuous screw thread having means cooperating witheach other to break the continuity of a foreign electric conductorpositioned to bridge the fuse within the fuse holder.

26. A fuse assembly comprising in com ination, a fuse holder, a fuse,screw threads carried by the fuse holder and the plug cooperating tocause interfitting engagement thereof and stop means on the respectivescrew threads cooperating with each other to limit the degree of suchinterfitting engagement.

27. A fuse assembly comprising in combination, a fuse holder, a fuse,cooperating screw threads on the fuse holder and on the fuse to effectremovable closely interfltting engagement thereof and means on thecooperating screw threads comprising saw teeth thereon, operable byrelative turning movement of the holder and the fuse to break thecontinuity of a foreign electric conductor positioned to bridge the fusewithin the fuse holder.

28. A fuse assembly comprising in combination, a fuse holder having asuccession of discontinuous screw threads therein, each of said screwthreads being relatively thin in an axial direction and havingrelatively abrupt leading ends, and a fuse having a screw disc at itsentering end, said screw disc having a relatively abrupt leading end tocooperate with the respective leading ends of the interrupted screwthreads to break the continuity of a foreign electric conductorpositioned to bridge the fuse within the fuse holder.

29. A fuse assembly comprising in combination, a fuse holder comprisinga shell of electricinsulating material, a plurality of axially-spaceddiscontinuous screw threads supported by the shell and projectingradially inwardly therefrom, a metal ring at the outer end of the shellhaving an inwardly extending screw thread integral therewith, certain ofsaid sets of screw threads having an abrupt leading end, an aperturedclosure plate of electric-insulating material at the inner end of saidshell and a metal shell clamping the closure plate and the metal ringagainst the shell of insulating material and a fuse having a screwthreaded body portion adapted to be screwed into the holder andcomprising a metal screw disc having an abrupt leading end cooperatingwith the leading ends of the discontinuous screw threads in the fuseholder to break the continuity of a foreign electric conductorpositioned to bridge the fuse within the fuse holder.

30. A fuse assembly comprising in combination, a fuse holder havingnon-current-carrying screw threads, one of which has a radially-inwardlyextending projection thereon and a fuse adapted to be screwed into thefuse holder and comprising a center contact of predetermined axiallength, and a metal screw disc having a leading and adapted to engagethe projection on the screw thread in the fuse holder to limit thedegree of interfitting movement of the fuse and fuse holder.

31. A fuse assembly comprising a fuse holder and a fuse adapted to bescrewed into said holder, the fuse holder and the fuse respectivelyinclud-. ing a plurality of lugs located adjacent to the inner and tothe outer peripheral surfaces thereof to plurally break during relativerotary movement of the fuse and fuse holder, the continuityof a foreignelectric conductor positioned to bridge the fuse within the fuse holder.

32. A fuse assembly comprising a fuse holder including a plurality oflugs spaced both peripherally and axially thereof at its inner peripheryand a fuse adapted to be screwed into the fuse holder and including aplurality of lugs spaced peripherally and axially thereof at its outerperiphery, said lugs in the fuse holder and on the fuse interfittingclosely with and moving past each other when the fuse is screwed intothe holder to break at a plurality of places a foreign electricconductor positioned to bridge the conductor within the fuse holder.

33. A fuse assembly including a fuse holder comprising a body ofelectric-insulating material and a plurality of axially spacedprojections extending inwardly of the body and a fuse adapted to fitinto the fuse holder and comprising a projection extending outwardlyfrom the fuse at its leading end and cooperating with the projections inthe body of the holder to break, at a plurality of spaced points, thecontinuity of a foreign electric conductor inserted in the fuse holder,when the fuse is fitted into the holder.

34. A fuse holder assembly comprising a plurality of insulation members,metallic screw threads fitted in the insulation members and meansexterior of the insulation members and metallic screw threads adapted tohold the insulation members and metallic screw threads in I position.

35. In an enclosed tamper-resistant fuse adapted to fit in atamper-resistant fuse-holder, a body of insulation material, a contactproject ing through the base, a contact projecting through an upper partof the body, remote from the base, said contacts being so arranged thata fuse link may be fitted in series therebetween within the body, saidcontacts being so spaced apart axially on the outside of the body as toleave a wide space of insulation aroundthe body which can be leftexposed to aid in preventing tampering, holding means on said spacearound the body arranged on the relative rotation of fuse andfuse-holder to co-act with means on a fuse-holder to hold their contactsin engagement, and abruptly extending means on the outside of the fuseto impair, during such rotation, the continuity of foreign electricalconducting material positioned between fuse and fuse-holder to bridgethe fuse.

36. In an enclosed tamper-resistant fuse adapted to fit in atamper-resistant fuse-holder, a body of insulation material, a fuse linkwithin the body, a contact extending through the base to the bottomthereof, a contact extending through an upper part of the body remotefrom the base, said contacts on the outside of the body being so spacedapart axially as to leave a substantial band of insulation around thebody which can be left uncovered to aid in preventing tampering, holdingmeans on'said band arranged, on the relative rotation of fuse andfuse-holder, to co-act with means on a fuseholder to hold their contactsin engagement, and abruptly extending means on the outside of the fuseto impair, during such rotation, the continuity of foreign electricalconducting material positioned between fuse and fuse-holder to bridgethe fuse.

3'7. In an enclosed tamper-resistant fuse adapted to fit in atamper-resistant fuse-holder, a body of insulation material, a contactthrough the base and a contact through an upper part of the body, remotefrom the base; the contacts being so arranged that a fuse link may befitted in series therebetween within the body; the contacts on theoutside of the body being so spaced apart axially as to provide arelatively wide space of insulation around the body which can be leftuncovered to aid in preventing tampering; threaded holding means,substantially free from current flow therethrough, on said space.adapted to co-act with threaded holding means on the fuse-holder,whereby the frictional engagement between the threads on fuse andfuse-holder may, by substantial relative rotation thereof, impair thecontinuity of foreign electrical conducting material positioned betweenfuse and fuseholder to bridge the fuse, while bringing the contacts onthe fuse into electrical connection with contacts on the fuse-holder.

38. An enclosed fuse arranged to resist the bridging thereof and adaptedto be fitted into a tamper-resisting fuse-holder; said fuse comprising abody of insulation material, a fuse link within the body, a contactextending through the base thereof and a second contact extendingthrough an upper part of the body and remote from the other contact; thecontacts being so spaced axially on the body as to leave a sub stantialband of insulation between the contacts, a disruptive means on the outerperiphery of the body so arranged that, on rotation of the fuse in thefuse-holder, the continuity of foreign electrical conducting materialplaced between fuse and fuse-holder to bridge the fuse may be impaired,and holding means between the contacts free from current flowtherethrough, arranged to co-act with means on the fuse-holder to holdthe fuse contacts in engagement with those on the fuse-holder.

39. An enclosed fuse adapted to be fitted into a tamper-resistantfuse-holder; said fuse having a body of insulation material, a fuse linkwithin the body, a contact projecting through the base thereof, acontact projecting through an upper part of the body; the contacts beingso spaced axially on the body that a substantially wide space around thebody of insulation can be left exposed, and holding means on the outsideof the fuse between the contacts and free from current flowtherethrough, and having a sharp surface at an angle to the line ofrotation of the fuse, so arranged that, on rotation thereof, suchholding means may cc-act with means on the fuse-holder to break thecontinuity of foreign electrical conducting material positioned betweenfuse and fuse-holder to bridge the fuse and to hold the contacts inengagement.

40. An enclosed fuse adapted to be fitted into a tamper-resistantfuse-holder; said fuse having a body of insulation material, a fuse linkwithin the body, a contact projecting through the base, a contactprojecting through an upper part of the body, remote from the othercontact, the contacts being so spaced apart axially that a relativelywide band of the insulation around the body can be left exposed, and aprojecting member on the outside of the fuse, independent of at leastone contact, so arranged on rotation thereof in a fuse-holder as toco-act with means on a fuse-holder to impair the continuity of foreignelectrical conducting material positioned between fuse and fuse-holderto bridge the fuse, and holding means between the contacts arranged toco-act with holding means on a fuseholder to hold the contacts inengagement.

41. .In an enclosed tamper-resistant fuseholder adapted to detachablyhold a tamperresistant fuse in an electric circuit, a hollow body ofinsulation material, a contact projecting through the base, a contact onan upper part of the body remote from the base; said contacts being sospaced apart axially as to leave a substantial band of insulation on theinside wall of the body which can be left uncovered to aid in preventingtampering, holding means between the contacts arranged, on the relativerotation of fuse and fuse-holder, to co-act with means on a fuse to holdtheir contacts in engagement, and abruptly extending means on the innerwall of the fuse-holder, to impair, during such rotation, the continuityof foreign electrical conducting material positioned between fuse andfuseholder to bridge the fuse.

42. In an enclosed tamper-resistant fuseholder adapted to detachablyhold a tamperresistant fuse in an electric circuit, a hollow body ofinsulation material, a metallic outer shell arranged to fit into astandard Edison screw socket, a contact projecting through the base, acontact on an upper part of the body remote from the base; said contactsbeing so spaced apart axially as to leave a substantial band ofinsulation on the inside wall of the body which can be left uncovered toaid in preventing tampering, holding means between the contactsarranged, on the relative rotation of fuse and fuseholder, to co-actwith means on a fuse to hold their contacts in engagement, and abruptlyextending means on the inner wall of the fuseholder, to impair, duringsuch rotation, the continuity of foreign electrical conducting materialpositioned between fuse and fuse-holder to bridge the fuse.

43. A fuse assembly, arranged to resist tamper= ing, comprising twomembers, each having a body of insulating material; one an enclosed fuseand the other a fuse-holder adapted to detachably hold the fuse in anelectric circuit; in each memher a contact projecting through the baseand a contact on the upper part of the body remote from the base; saidcontacts being so spaced apart axially as to leave a substantially wideband of insulation around the body which can be left uncovered, meansbetween the contacts on each member substantially free from current flowtherethrough, arranged to co-act upon a relative rotation of the membersto bring their contacts into engagement, and to impair the continuity offoreign electrical conducting material positioned between the members tobridge the fuse.

44, A fuse assembly, arranged to resist tampering, comprising twomembers, each having a body of insulating material; one an enclosed fuseand the other a fuse-holder adapted to detachably hold the fuse in anelectric circuit; in each member a contact projecting through the baseand a contact on the upper part of the body remote from the base; saidcontacts being so spaced apart axially as to leave a substantially wideband of insulation around the body which can be left uncovered, meansbetween the contacts on each member substantially free from current flowtherethrough, arranged to co-act upon a relative rotation of the membersto bring their contacts into engagement, and means on the membersco-acting to impair the continuity of foreign electrical conductingmaterial positioned between the members to bridge the fuse.

ALOYSIUS B. BUSSMANN.

